The present invention relates to one part heat curable organopolysiloxane compositions having improved shelf stability. More particularly, the present invention relates to the employment of a hydrosilylation catalyst in the form of an inclusion compound of a cyclodextrin, such as .beta.-cyclodextrin and a silicone soluble complex of a platinum group metal material, platinum metal, a C.sub.(1-4) alkyl substituted platinum metal, or a rhodium halide, in combination with a complexing ligand selected from the class consisting of a cyclopentadiene, a 1,5-cyclooctadiene and a norbornadiene.
Prior to the present invention, as shown by Kookootsedes et al, U.S. Pat. No. 3,445,420, one component organopolysiloxane compositions were based on a platinum catalyzed silicon hydride-silicon vinyl addition reaction which generally utilized an inhibitor for the platinum catalyst. The purpose of the inhibitor was to slow down the hydrosilylation reaction to increase the work life of the one component organopolysiloxane mixture at low or room temperatures. The organopolysiloxane mixtures were generally composed of a base polymer consisting of a polydiorganosiloxane having chemically combined methylvinylsiloxy units which was used in combination with a siliconhydride siloxane. Additional inhibited one package silicon hydride-silicon vinyl platinum addition curable organopolysiloxane compositions are shown by Berger et al, U.S. Pat. No. 3,882,083, utilizing an ethylenically unsaturated isocyanurate as an inhibitor, and U.S. Pat. Nos. 4,472,562, and 4,472,563 employing acetylenic unsaturated inhibitors.
In copending application Ser. No. 07/364,557, filed May 22, 1989, now U.S. Pat. No. 4,960,626, one part heat curable organopolysiloxane compositions are described utilizing a platinum catalyst which is microencapsulated in an organic resin, such as a thermoplastic organic polymer, or a thermosetting organic polymer. The microencapsulated catalyst is in the form of capsules having an average diameter of about 4-60 microns. Although satisfactory shelf stability under ambient conditions can be achieved with the use of such microencapsulated platinum catalysts in one part mixtures of a vinyl-substituted polydiorganosiloxane fluid and a siloxane hydride fluid, it has been found that the capsules often settle to the bottom of the one part heat curable organopolysiloxane mixture, or reduce the transparency of the curable mixture.
In copending application Ser. No. 07/424,022,now U.S. Pat. No. 5,025,073, one part heat curable organopolysiloxane compositions are described which utilize as a latent platinum catalyst, an inclusion compound of a cyclodextrin, such as a .beta.-cyclodextrin, with a complex of a platinum halide and a diene, such as 1,5-cyclooctadiene (COD). Although valuable results can be obtained with the use of such inclusion compounds of a cyclodextrin and a platinum halide complex, one part silicone mixtures containing such inclusion compounds often suffer from the appearance of irregular black spots due to the poor solubility of the released platinum complex into the silicone RTV. In addition, the physical properties of one part RTV silicone compositions containing such cyclodextrin inclusion compounds are often inferior to the properties of the corresponding two part RTVs containing a soluble platinum catalyst.
It would be desirable, therefore, to develop one part heat curable organopolysiloxane compositions having satisfactory shelf stability which provide organopolysiloxanes substantially equivalent to 2 part heat curable RTVs when in the cured state.